1. Field of the Invention
The present invention relates to a laser irradiation device and a laser induced thermal imaging method, and more particularly, to a laser irradiation device including a laser generator for patterning and a laser generator for preheating, and a laser induced thermal imaging method.
2. Description of the Related Art
In general, an organic light emitting diode (OLED) includes an anode electrode, a cathode electrode, and organic layers interposed between the anode and cathode electrodes. Such an OLED is classified into a polymer OLED and a small molecule OLED according to a material of forming the organic layer, in particular, an emission layer.
In order to realize a full color OLED, the emission layer should be patterned, and a method of using a shadow mask is employed in the small molecule OLED and an ink-jet printing or Laser Induced Thermal Imaging (hereinafter, referred to as an LITI) method is employed for patterning the emission layer. Among these methods, the LITI has advantages in that the organic layer can be finely patterned and a large-area and high resolution display can be easily realized. The LITI also has an advantage in that a dry process is used, whereas a wet process is used in the ink-jet printing method.
The LITI is a transfer method using laser, which requires at least a light source, a substrate, and a donor substrate to form the organic layer using the method. A laser beam generated in a laser irradiation device is used as the light source. This is disclosed in Korean Patent Application No. 1998-51844, and U.S. Pat. Nos. 5,998,085, 6,214,520, and 6,114,088.
A conventional laser irradiation device and LITI method include a donor substrate 150 being laminated on an acceptor substrate where predetermined elements are formed. The donor substrate is composed of a base substrate, a light-to-heat conversion layer formed on the base substrate, and a transfer layer formed on the light-to-heat conversion layer.
In this case, a laser beam generated by a laser irradiation device is used as a light source for irradiating light onto the donor substrate.
The laser irradiation device includes a laser generator, a patterned mask, and a projection lens.
The laser generator is used to irradiate the laser beam onto a predetermined region of the base substrate. In this case, the laser beam generated by the laser generator passes through the patterned mask, and the passed laser beam is refracted by the projection lens to be irradiated onto the base substrate. The laser beam is blocked in an unpatterned portion of the mask.
The laser beam irradiated onto the predetermined region of the base substrate is absorbed by the light-to-heat conversion layer to be converted into thermal energy. A gas is generated in the light-to-heat conversion layer by the absorbed thermal energy, which causes the light-to-heat conversion layer to be swollen. The swollen light-to-heat conversion layer causes the transfer layer to be adhered onto the acceptor substrate, and the adhered transfer layer is disconnected from the donor substrate, so that the transfer layer is transferred onto the acceptor substrate.
In this case, when temperature excessively increases due to the delivered thermal energy, the transfer layer may be degraded. A laser beam having high intensity may be used to prevent the transfer layer from being degraded, however, the transfer layer is partially disconnected in a portion having a step formed in the acceptor substrate so that the transfer is not carried out on the portion. This is called an edge open failure or an untransferred failure. This is because the laser beam is irradiated for a short time so that the temperature of the light-to-heat conversion layer does not increase enough to cause the transformation.